I cannot see the problem for authors to use XHTML syntax to mix
(X)HTML with SVG. Many authors switched anyway already from
HTML to XHTML to make a difference.
Beeing able to use SVG inside proper XHTML might be a big
stimulation for many authors to switch from tag-soup-production
to proper markup ;o)
This could be the contribution from SVG to clean up future
(X)HTML from tag-soup-nonsense in the next years ;o)